Epoxy resin composition for fiber-reinforced composite material prepreg, and fiber-reinforced composite material

ABSTRACT

The present invention relates to an epoxy resin composition for a fibre reinforced composite material, which is thermosetting resin composition where the glass transition temperature Tg of the cured material obtained by heating for 2 hours at 180° C. is at least 150° C., and the modulus of rigidity G′ R  in the rubbery plateau in the temperature region above the aforesaid Tg is no more than 10 MPa. In accordance with the present invention, it is possible to provide a fibre-reinforced composite material which is outstanding in its resistance to hot-wet environmental condition, impact resistance, and strength characteristics such as tensile strength and compression strength, and furthermore it is possible to provide a thermosetting resin composition and a prepreg outstanding in terms of their peel strength to a honeycomb core.

TECHNICAL FIELD

The present invention relates to an epoxy resin composition, to prepregand to fibre-reinforced composite materials. More particularly, itrelates to prepreg, fibre-reinforced composite materials and honeycombsandwich panels, and to the epoxy resin composition employed as thematrix resin therein, favourably used in the production of structureswhere, as advanced composite materials, high levels ofcompression/tensile strength and tensile/flexural modulus are demanded,together with high levels of specific strength and specific moduluscomprising these properties divided by specific gravity.

TECHNICAL BACKGROUND

Fibre-reinforced composite materials have outstanding mechanicalproperties and are widely used in aircraft, in motor vehicles and inindustrial applications but, as their applications have become more andmore diverse, so have the property requirements placed on them.

Fibre-reinforced composite materials are heterogeneous materials inwhich the essential constituents are reinforcing fibre and matrix resin,and so there are considerable differences between the properties in thefibre axial direction and the properties in other directions. Thus, theresistance to a drop-weight impact is governed by the interlaminardelamination strength which is determined for example by theinterlaminar edge delamination strength, so it is well known that merelyincreasing the strength of the reinforcing fibre does not lead tofundamental improvements. In particular, fibre-reinforced compositematerials in which the matrix resin is a thermosetting resin reflect thelow toughness of the matrix resin and tend to show ready failure in thecase of stresses applied in other than the fibre axial direction. Hence,in addition to improving the properties in the fibre axial direction,various techniques have been proposed with the objective of improvingthe composite material properties in directions other than that of thefibre axis.

As a means for enhancing the toughness of the thermosetting resinitself, there is disclosed in U.S. Pat. No. 4,656,208 the addition of anaromatic thermoplastic resin oligomer to the epoxy resin, and it is saidthat impact strength of the fibre-reinforced composite material is alsoimproved.

Furthermore, in U.S. Pat. No. 3,472,730 (1969), there is disclosed theimprovement of the interlaminar delamination strength by providing aseparate exterior film comprising an elastomer-modified thermosettingresin at one or both faces of a fibre-reinforced sheet.

However, not only is the improvement effect in terms of the interlaminardelamination strength and the like inadequate, these methods also eachhave their own disadvantages.

In the method of enhancing the resin toughness by the addition of anaromatic thermoplastic resin such as a polysulphone, an increase in theresin viscosity is unavoidable, so that either the impregnation of thefibre is inadequate or, alternatively, prepreg thoroughly impregnatedwith resin is inferior in its handling characteristics in that its drapeis unsatisfactory. Furthermore, as the amount of thermoplastic resin isincreased, the solvent resistance of the cured product is reduced.

Moreover, in the method in which there is interposed film containingelastomer-modified thermosetting resin, as the elastomer content isincreased so the heat resistance of the composite material obtainedfalls considerably while, conversely, as the elastomer content isreduced so there is a marked deterioration in the interlaminardelamination strength improvement effect.

As an attempt to resolve such problems, prepregs have been proposed withresin fine particles dispersed at the surface. For example, in U.S. Pat.No. 5,028,478, there is disclosed a technique for providing a toughcomposite material of good heat resistance using fine particles of athermoplastic resin such as nylon.

However, in the method disclosed in U.S. Pat. No. 5,028,478, because ofthe high dependence on the toughness of the thermoplastic resin itself,when the composite material is exposed to severe environmentalconditions for a long time, and/or when there is poor affinity betweenthe fine particles of thermoplastic resin and the bulk resin,interfacial separation between the bulk resin/fine particles is broughtabout and there is a danger of a considerable lowering in the toughnessbetween layers.

In European Unexamined Patent Publication Nos 377,194 and 392,348, thereare disclosed techniques for providing a composite material which isoutstanding it its heat resistance and toughness by using thermoplasticresin fine particles of polyimide or polyethersulphone. The fineparticles used dissolve in the bulk resin at the time of the prepregcuring, to form a thermoplastic resin layer, and the toughness of thecomposite material is enhanced by this. However, in these technologies,since there is employed a means in which thermoplastic resin fineparticles dissolve in the bulk resin, the internal state of thefinally-formed fibre-reinforced composite material, and in particularthe interlaminar thickness between the layers of composite materialcomprising prepreg or the like, is markedly influenced by changes in thefabrication conditions such as the pressure and the rate of temperaturerise, and so there is the disadvantage that the properties of thecomposite materials obtained are unstable.

Now, in the case of aircraft structural materials or interior materials,from the point of view of reducing weight there has been increasing useof honeycomb sandwich panels in which the skin panels arefibre-reinforced composite materials. Here, the honeycomb sandwichpanels are generally produced by so-called co-cure fabrication, in whichthere is used an aramid honeycomb, glass honeycomb or aluminiumhoneycomb as the honeycomb core, and prepregs for forming the skinpanels are laid on both faces thereof, after which the curing of theresin and adhesion to the honeycomb core are simultaneously effected.

In said co-cure fabrication, hitherto there has mostly been used afabrication method in which an adhesive film is interposed between thehoneycomb core and prepreg laminate but, recently, from the point ofview of further reducing the weight of the honeycomb sandwich panel andlowering cost, there has been a demand for a so-called self-adhesivetechnology in which the honeycomb core and the prepreg are directlyaffixed. However, in cases where no adhesive film is used, the resincontained in the prepreg needs to bear the burden of adhesion to thehoneycomb core, and so it has been difficult to ensure good adhesion.

As a honeycomb fabrication method relating to prepreg in which carbonfibre is the reinforcing fibre, and relating to the matrix resin, U.S.Pat. No. 4,500,660 discloses an epoxy resin composition which containsthe reaction product of a specified epoxy resin and abutadiene-acrylonitrile copolymer with functional groups at bothterminals, plus dicyandiamide as a curing agent, for the purposes ofimproving the peel strength to the honeycomb core and the interlaminarshear strength in terms of the skin panels. However, while it ispossible by the technology described in U.S. Pat. No. 4,500,660 tomaintain, to a certain degree, high levels of room temperature strengthproperties such as tensile strength in the composite material obtained,the peel strength between the prepreg and the honeycomb core is stillinadequate and there is the disadvantage of poor wet heat resistance.

The present invention aims to offer fibre-reinforced composite materialswhich can be used favourably in applications where high level propertiesare demanded in a hot and wet environment in particular, and which areoutstanding in their impact resistance and various characteristics ofstrength such as tensile strength, compression strength and interlaminardelamination strength; and also an epoxy resin composition and prepregwith outstanding handling properties which can be suitably employed inthe production of such fibre-reinforced composite materials; and prepregwhich is outstanding in its peel strength to a honeycomb core.

DISCLOSURE OF THE INVENTION

In order to overcome the aforesaid problems, the present invention hasthe following constitution. That is to say, it is an epoxy resincomposition for a fibre-reinforced composite material, where the glasstransition temperature Tg of the cured material obtained by heating for2 hours at 180° C. is at least 150° C., and the modulus of rigidityG′_(R) in the rubbery plateau in the temperature region above theaforesaid Tg is no more than 10 MPa.

Furthermore, in order to resolve the aforesaid problems the presentinvention also has the following constitution. Specifically, it is aprepreg formed by the impregnation of reinforcing fibre with an epoxyresin composition which includes the following constituents [A], [B] and[C], plus curing agent, and the respective contents per 100 parts byweight of the total epoxy resin in said resin composition are 5 to 35parts by weight of constituent [A] and 50 to 95 parts by weight ofconstituent [B], and at least 90% of the constituent [C] is containedwithin a depth, from the prepreg surface, of 20% of the average prepregthickness.

[A] trifunctional epoxy resin and/or tetrafunctional epoxy resin

[B] difunctional epoxy resin

[C] fine particles of average particle size 3 to 70 μm which aresubstantially insoluble in the epoxy resin of the aforesaid resincomposition.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1: A conceptual diagram of the Tg measurement by DSC

FIG. 2: A conceptual diagram of the G′_(R) measurement by DMA

FIG. 3: A sectional schematic diagram (partial) of laminate

EXPLANATION OF THE NUMERICAL CODES

1: endotherm direction

2: exotherm direction

3: glass transition temperature Tg

4: temperature

5: modulus of rigidity G

6: glassy region

7: glass transition region

8: rubbery region

9: rubbery plateau modulus of rigidity G′_(R)

10: temperature

11: line segments

12: interlaminar region

13: thickness of composite material layer

14: standard 0° layer

15: set range

Optimum Form for Practising the Invention

As a result of a painstaking investigation the present inventors havefound that, by employing an epoxy resin composition where the glasstransition temperature Tg of the cured material obtained by heating saidepoxy resin composition for 2 hours at 180° C. (hereinafter this is justreferred to as the Tg) is above a specified temperature, and the modulusof rigidity G′_(R) for the rubbery plateau in the temperature regionabove the aforesaid Tg of the cured material is below a specifiedtemperature, the aforesaid problems associated with the fibre-reinforcedcomposite material impact resistance and resistance to hot-wetenvironmental condition, the enhancement of various measures of strengthsuch as the interlaminar delamination strength and the enhancement ofthe adhesive strength to the honeycomb core, are all resolved.

Furthermore, while the tensile strength of a fibre-reinforced compositematerial in the fibre direction (hereinafter referred to as the 0°tensile strength) is generally greatly dependent on the tensile strengthof the reinforcing fibre itself, it is usually lower than the valuecalculated from the strand tensile strength of the reinforcing fibreitself. However, the present inventors have discovered that, byemploying the aforesaid resin composition of the present invention asthe matrix resin for a prepreg or composite material, the inherentstrength characteristics of the reinforcing fibre may be fully utilizedand, in the composite material obtained, the 0° tensile strength ismarkedly enhanced.

In the present invention, the Tg is the value measured by means of adifferential scanning calorimeter (DSC) method as described below, andit needs to be at least 150° C., preferably at least 160° C. and morepreferably at least 165° C. If it is less than 150° C., then the heatresistance of the composite material obtained will be inadequate.Furthermore, from the point of view of the composite material impactresistance, tensile strength and other measures of strength, and theresistance to peeling from a honeycomb core (referred to below merely asthe peel strength), it is preferred that the Tg be less than 210° C. anddesirably less than 200° C. Again, in the present invention, G′_(R) isthe value of the modulus of rigidity measured in the rubbery plateau inthe temperature region above the Tg by dynamic mechanical analysis (DMA)as described below, and it needs to be no more than 10 MPa, preferablyno more than 9 MPa and more preferably no more than 8 MPa. If it exceeds10 MPa, then in the composite material obtained, the impact resistance,the strength characteristics such as the tensile strength, and the peelstrength from a honeycomb core, are reduced.

Furthermore, from the point of view of enhancing the impact resistance,the strength characteristics such as tensile strength, and the peelstrength from a honeycomb core, it is preferred that there be used anepoxy resin composition where the tensile breaking strain of the resincured material is at least 8%. More preferably, there is used an epoxyresin composition where the tensile breaking strain is at least 10%.

From the point of view of enhancing the composite material compressioncharacteristics, shear characteristics and the peel strength from ahoneycomb core, it is preferred that the amount of epoxy resinincorporated in the epoxy resin composition of the present invention beat least 55 wt %, preferably at least 65 wt % and more preferably atleast 75 wt %, in terms of the total 100% of resin composition.

As an epoxy resin, there is preferably used a difunctional epoxy resinwith two epoxy groups per molecule, and as examples of the difunctionalepoxy resins which can be used there are the bisphenol A type epoxyresins and bisphenol F type epoxy resins, and biphenyl type epoxyresins, naphthalene type epoxy resins, dicyclopentadiene type epoxyresins and diphenylfluorene type epoxy resins which give rigid resins ofgood resistance to hot-wet environmental condition, or combinations ofthese. In the present invention, the difunctional epoxy resin isconstituent [B].

Examples of the bisphenol A type epoxy resins which can be used includeEpikote 827 (epoxy equivalent: 180-190), Epikote 828 (epoxy equivalent:184-194), Epikote 1001 (epoxy equivalent: 450-500), Epikote 1004 (epoxyequivalent: 875-975) (registered trade names; produced by Yuka ShellEpoxy K.K.), YD128 (epoxy equivalent: 184-194) (produced by the TotoChemical Co.), Epiclon 840 (epoxy equivalent: 180-190), Epiclon 850(epoxy equivalent: 184-194), Epiclon 855 (epoxy equivalent: 183-193),Epiclon 860 (epoxy equivalent: 230-270), Epiclon 1050 (epoxy equivalent:450-500) (registered trade names; produced by Dainippon Ink & ChemicalsInc.), ELA 128 (epoxy equivalent: 184-194) (produced by the SumitomoChemical Co.) and DER331 (epoxy equivalent: 184-194) (produced by theDow Chemical Co.).

Examples of the bisphenol F type epoxy resins which can be used includeEpiclon 830 (epoxy equivalent: 165-185) (registered trade name; producedby Dainippon Ink & Chemicals Inc.) and Epikote 807 (epoxy equivalent:160-175) (registered trade name; produced by Yuka Shell Epoxy K.K.).

Furthermore, as a biphenyl type epoxy resin there can be used YX4000(epoxy equivalent: 180-192) (produced by Yuka Shell Epoxy K.K.), as anaphthalene type epoxy resin there can be used HP-4032 (epoxyequivalent: 140-150) (produced by Dainippon Ink & Chemicals Inc.), as adicyclopentadiene type epoxy resin there can be used EXA-7200 (epoxyequivalent: 260-285) (produced by Dainippon Ink & Chemicals Inc.), andas a diphenylfluorene type epoxy there can be used EPON HPT1079 (epoxyequivalent: 250-260) (trade name; produced by Shell).

In the present invention, in order to produce a cured material which isrigid and has good resistance to hot-wet environmental condition, thereis preferably used as epoxy resin an epoxy resin which is at leasttrifunctional, having three or more epoxy groups per molecule.

In the present invention, a trifunctional epoxy resin and/ortetrafunctional epoxy resin constitutes constituent [A].

As trifunctional epoxy resins or tetrafunctional epoxy resins, there canbe used for example phenol novolak type epoxy resins, cresol novolakepoxy resins, glycidylamine type epoxy resins such as tetraglycidyldiaminodiphenylmethane, triglycidyl aminophenol or triglycidylaminocresol, glycidyl ether type epoxy resins such astetrakis(glycidyloxyphenyl)-ethane or tris(glycidyloxy)methane, ormixtures thereof.

As phenol novolac type epoxy resins, there can be used for exampleEpikote 152 (epoxy equivalent: 172-179) or Epikote 154 (epoxyequivalent: 176-181) (registered trade names; produced by Yuka ShellEpoxy K.K.), DER438 (epoxy equivalent: 176-181) (produced by DowChemical Co.), EPN1138 (epoxy equivalent: 176-181) or 1139 (epoxyequivalent: 172-179) (trade names, produced by Ciba Geigy).

As cresol novolac type epoxy resins, there can be used for exampleESCN220L (epoxy equivalent: 200-230) (produced by the Sumitomo ChemicalCo.), Epikote 180S65 (epoxy equivalent: 205-220) (registered trade name,produced by Yuka Shell Epoxy K.K.), or ECN1273 (epoxy equivalent: 225)(produced by Ciba Geigy).

As the tetraglycidyl diaminodiphenylmethane, there can be used forexample ELM434 (produced by the Sumitomo Chemical Co.), YH434L (producedby the Toto Chemical Co.), or Epikote 604 (registered trade name,produced by Yuka Shell Epoxy K.K.).

As the triglycidyl aminophenol or triglycidyl aminocresol, there can beused ELM100 (produced by the Sumitomo Chemical Co.), MY0510 (produced byCiba Geigy), Epikote 630 (registered trade name, produced by Yuka ShellEpoxy K.K.) or the like.

In the present invention, it is preferred that there be included thefollowing percentages by weight of the epoxy resins, namely constituent[A] and constituent [B], per 100 wt % of total epoxy resin.

[A] trifunctional epoxy resin and/or tetrafunctional epoxy resin 5 to 35wt %

[B] difunctional epoxy resin 50 to 95 wt %

If there is less than 5 wt % of [A], then the wet heat resistance of thecomposite material obtained may be reduced, while if the amount exceeds35 wt % then the 0° tensile strength and the edge delamination strength(EDS) of the composite material obtained may be lowered. From this pointof view, the amount of [A] component more preferably lies in the range 5to 25 wt %.

Furthermore, with regard to [B], if the amount thereof is less than 50wt %, then the 0° tensile strength and the edge delamination strength(EDS) of the composite material obtained may be lowered, while if itexceeds 95 wt % then the wet heat resistance of the composite materialobtained may be reduced. From this point of view, in the presentinvention the amount of [B] component more preferably lies in the range70 to 95 wt %.

Now, as well as the aforesaid polyfunctional epoxy resins, there mayalso be used a small amount of monofunctional epoxy resin having onlyone epoxy group in the molecule, providing this is within a range thatdoes not impair the resistance to hot-wet environmental condition.

The curing agent for epoxy resin used in the present invention is notparticularly restricted providing it is a compound having active groups,which can react with epoxy groups. Specific examples are aromatic aminessuch as diaminodiphenylmethane and diaminodiphenylsulphone, aliphaticamines, imidazole derivatives, dicyandiamide, tetramethylguanidine,thiourea-added amines, carboxylic acid anhydrides such asmethylhexahydrophthalic anhydride, carboxylic acid hydrazides,carboxylic acid amides, polyphenol compounds, novolak resins,polymercaptans and the like. Furthermore, as a curing catalyst jointlyused with the curing agent, there can be employed for example aso-called Lewis acid complex such as the boron trifluoride ethylaminecomplex. Now, where these curing agents are micro-encapsulated, thestorage stability of the intermediate substrate material such as theprepreg is improved in, so this may be favourably employed.

A suitable curing accelerator can be used in combination with thesecuring agents to enhance the curing activity. Specifically, there can becited the example of the use of an imidazole derivative or a ureaderivative such as 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) as acuring accelerator in combination with dicyandiamide, and the example ofthe use of a tertiary amine as a curing accelerator in combination witha carboxylic acid anhydride or a novolak resin.

For the purposes of adjusting the viscosity of the resin composition orenhancing the storage stability, there may also be incorporated into theresin composition a compound obtained by preliminary reaction betweenthe epoxy resin and curing agent.

In the present invention, it is appropriate to incorporate into theresin composition from 1 to 20 wt % and preferably 2 to 10 wt % ofbisphenol compound per 100 wt % of the total epoxy resin. With less than1 wt %, the peel strength, and the tensile strength of the compositematerial obtained, may be lowered, while with more than 20 wt % thetackiness of the prepreg may be lowered and the resistance to hot-wetenvironmental condition and compression strength of the compositematerial obtained may be reduced.

Examples of the bisphenol compound here are bisphenol A, bisphenol F,bisphenol S, bisphenol AD, bisphenol Z, bisphenolfluorene anddihydroxybiphenyl, and alkyl- or halogen-substituted such compounds mayalso be favourably employed. Furthermore, as the bisphenol compoundthere can also be used dihydroxynaphthalene, dihydroxyanthracene or thelike. Of these, bisphenol S is outstanding in terms of its effect inenhancing the peel strength, the composite material tensile strength,and the resistance to hot-wet environmental condition and elongation ofthe cured material obtained by heating the resin composition (this isreferred to below just as the cured material), and so it is preferred.

In the present invention, it is possible to incorporate a thermoplasticresin into the resin composition in order to provide the effects ofenhancing the physical properties demanded of the cured material such astoughness and suppressing the occurrence of defects such as voids in lowpressure fabrication. Examples of the thermoplastic resins are thosewith bonds in the main chain selected from carbon-carbon bonds, amidebonds, imide bonds (for example polyetherimides), ester bonds, etherbonds, siloxane bonds, carbonate bonds, urethane bonds, urea bonds,thioether bonds, sulphone bonds, imidazole bonds and carbonyl bonds. Ofthese, thermoplastic resins with sulphone bonds such aspolyethersulphones are preferred from the point of view of enhancing theresistance to hot-wet environmental condition, the impact resistance andthe adhesion to the reinforcing fibre in the case of the cured materialor composite material obtained.

Now, the thermoplastic resin may also be a so-called oligomer. In suchcircumstances, from the point of view of preventing excessive resinviscosity at the time of fabrication and preventing impaired flowproperties, the number average molecular weight of the oligomer shouldbe no more than 10,000, and preferably no more than 7,000. Furthermore,from the point of view of the modification effect by the thermoplasticresin and maintaining the impact resistance of the composite materialobtained, the number average molecular weight of the oligomer should beat least 3,000 and preferably at least 4,000. Again, the oligomerpreferably has, at the terminals or within the molecular chain,functional groups which can react with the thermosetting resin. Asexamples of such thermoplastic resin oligomers, there are those whichcombine heat resistance and toughness such as polysulphone,polyethersulphone, polyetherimide, polyimide, polyamide, polyamideimideand polyphenylene ether.

There should be incorporated 5 to 20 parts by weight and preferably 8 to15 parts by weight of the thermoplastic resin per 100 parts by weight oftotal epoxy resin. If there is less than 5 parts by weight, then thetoughness of the cured material may be insufficient, while if the amountexceeds 20 parts by weight then the resin flow properties may beimpaired.

In the present invention, resin fine particles can be incorporated intothe resin composition in order to enhance the peel strength, and theimpact resistance of the composite material obtained. Fine particles ofaverage particle size 3 to 70 μm, and which are substantially insolublein the epoxy resin of the aforesaid resin composition, are constituent[C] of the present invention.

It is necessary that, in the composite material fabricating process,constituent [C] be substantially insoluble in the epoxy resin of theresin composition containing constituents [A] and [B]. Here,“substantially insoluble” means that, within the range from roomtemperature 25° C. up to the epoxy resin curing temperature, theproportion thereof dissolved-out into the fluid resin compositionproduced by uniformly mixing together the epoxy resins of the resincomposition containing aforesaid constituents [A] and [B] is less than10 wt %, preferably less than 5 wt %, and more preferably less than 2 wt%, in terms of the total 100 wt % of constituent [C].

The fine particles of constituent [C] will appropriately have an averageparticle size in the range 3 to 70 μm prior to incorporation into theresin composition, but there can be employed any fine particles theaverage particle size of which remains in the range 3 to 70 μm as aresult of swelling in the composite material fabrication process or as aresult of the dissolving-away into the bulk resin of a very small amountof the surface.

Insofar as they are substantially insoluble in the epoxy resin of theresin composition, constituent [C] may be organic fine particlescomprising an organic material or they may be inorganic fine particlescomprising metal or inorganic material but, from the point of view ofthe affinity to the bulk resin, organic fine particles are preferred.

In particular, thermoplastic resin fine particles or thermosetting resinfine particles are preferably used as the fine particles. Asthermoplastic resin fine particles, there are those comprisingthermoplastic resins having in the main chain bonds selected fromcarbon-carbon bonds, amide bonds, imide bonds, siloxane bonds, esterbonds, ether bonds, carbonate bonds, urethane bonds, urea bonds,thioether bonds, sulphone bonds, imidazole bonds and carbonyl bonds,examples of which are polyamide, polycarbonate, polyacetal,polyphenylene oxide, polyphenylene sulphide, polyarylate, polyester,polyamideimide, polyetherimide, polysiloxane, polysulphone,polyethersulphone, polyetheretherketone, polyaramid, polybenzimidazole,polyacrylate, polystyrene, polymethyl methacrylate (PMMA),benzoguanamine/melamine and the like.

It is preferred that the thermoplastic resin fine particles have atleast a partially crystalline structure and/or crosslinked structure. Inthis way, dissolution in the bulk resin is reduced and the form of theparticles is readily maintained in the matrix resin of the compositematerial.

Furthermore, specific examples of the thermosetting resin fine particlesare fine particles of one or more type selected from the groupcomprising phenolic resins, epoxy resins, melamine resins, polyimideresins, maleimide resins, cyanate resins and furan resins. Of these, theepoxy resin fine particles are outstanding in their affinity to the bulkresin, while phenolic resin fine particles have high heat resistance,and so these are respectively preferred.

On the other hand, fine powdered silica is an example of inorganic fineparticles. It is preferred that fine powdered silica be incorporatedinto the resin composition within a range such that the toughness andtensile elongation of the composite materials obtained are not impaired.

In the prepreg of the present invention, the aforesaid resin fineparticles [C] should be located in the vicinity of the prepreg surface.In this way, the peel strength estimated from the compoundingproportions is markedly exceeded and the impact resistance of thecomposite material obtained is enhanced. Here, “located in the vicinityof the surface” means that at least 90% of the resin fine particlescontained in the resin composition are distributed within a depth, fromthe prepreg surface, comprising 20%, preferably 15% and more preferably10% of the average thickness of the prepreg.

In this way, in the case where prepregs are laminated and the resincured to produce a composite material, interlaminar regions betweenlayers of cured prepreg, that is to say composite material layers andadjacent composite material layers, are readily formed and, as a result,the composite material obtained shows high EDS and impact strength.

As disclosed in U.S. Pat. No. 5,028,478, prepregs with resin fineparticles localized at the surface can be produced by methods such asthe method of putting the resin fine particles to the prepreg surface,the method of impregnating the reinforcing fibre with a resincomposition in which the resin fine particles are uniformly blended, andthe method of affixing a resin film containing a high concentration ofresin fine particles to the prepreg surface.

The average particle size of the resin fine particle should be in therange from 3 to 70 μm, preferably 10 to 70 μm and more preferably 25 to60 μm. If it is less than 3 μm, the fine particles will find their wayinto the gaps between reinforcing fibres, and in the composite materialobtained the impact resistance enhancement effect will be diminished,while if it exceeds 70 μm, the arrangement of the reinforcing fibre willbe disrupted and the interlaminar regions in the composite materialobtained by lamination of the prepreg obtained will be thicker thannecessary, so the properties of the composite material may be lowered.

The form of the resin fine particles may be that of a fine powderobtained by the pulverizing of resin, or may comprise particles obtainedby the spray drying method or the re-precipitation method, and the fineparticles may also be irregularly shaped as well as spherical. Inaddition, they may be porous, or they may be fibrous or needle shaped.

From the point of view of facilitating the mixing with the epoxy resinand preventing any lowering of the tack/drape properties of the prepregobtained, there should be used from 1 to 15 wt % of the resin fineparticles per 100 wt % of the total resin composition, and from thepoint of view of enhancing the impact strength, peel resistance, peelstrength, and the compression strength of the composite materialobtained, from 3 to 12 wt % is preferred.

Furthermore, in the present invention, for Theological control of theresin composition, inorganic fine particles such as finely powderedsilica can be incorporated into the resin composition within a rangesuch that the toughness and elongation of the cured material are notimpaired. Again, a polymaleimide resin or resin with cyanate esterterminals can be incorporated within a range such that the toughness ofthe cured material is not impaired. Moreover, there can also beincorporated a monofunctional epoxy, an acrylate ester or other suchreactive diluent, or an elastomer or other such modifier, within a rangesuch that the wet heat resistance of the cured material is not impaired.

The polymaleimide used is, for example, a compound containing an averageof at least two maleimide groups at the terminals, produced by the knownmethod of reacting a diamine with an equivalent amount of unsaturateddicarboxylic acid anhydride. Furthermore, as the resin with cyanateester terminals, there can be used the cyanate ester of a polyhydricphenol such as bisphenol A.

As elastomers, there can be used for example butadiene-acrylonitrilerubber, styrene-butadiene rubber or butyl acrylate.

In the prepreg of the present invention there is preferably usedreinforcing fibre, which comprises continuous fibre. Moreover, thereinforcing fibre will preferably be outstanding in its wet heatresistance and tensile strength. Specific examples are carbon fibre,graphite fibre, aramid fibre, silicon carbide fibre, alumina fibre andboron fibre. Of these, carbon fibre and graphite fibre are preferred inthat they are of excellent specific strength and specific elasticmodulus, and they contribute markedly to a lowering of the weight of thecomposite material obtained. The carbon fibre or graphite fibre shouldhave a tensile strength of 4.4 GPa or more, preferably 4.9 GPa or more,and the tensile elongation should be at least 1.5% and preferably atleast 2.0%.

The reinforcing fibre comprising continuous fibre should have a fibrelength of at least 5 cm and preferably at least 7 cm. If it is less than5 cm, then the strength properties of the composite material obtainedmay be lowered.

The form of the reinforcing fibre may be that ofunidirectionally-oriented fibre or randomly-oriented fibre, orsheet-shape, mat-shape, woven, braided or the like. Of these,unidirectionally-oriented fibre is favourable from the point of view ofobtaining composite material with outstanding specific strength andspecific elastic modulus, while in the case of the production of theskin panels of a honeycomb sandwich panel via prepregs, woven materialis preferred in terms of the ease of handling and excellent peelstrength.

The fibre-reinforced material of the present invention can be producedfor example by laying-up the prepreg of the present invention asdescribed above, in a specified shape, and then curing the resin byapplying heat and pressure.

The fibre-reinforced composite material of the present invention isformed by the lamination of a plurality of layers of composite materialcomprising reinforcing fibre and aforesaid thermosetting resin, and thethickness of the interlaminar regions formed between the aforesaidcomposite material layers is preferably in the range 10 to 70 μm. If theinterlaminar thickness is less than 10 μm then, while the rigiditypossessed by the matrix resin contributes to the high performance of thecompression strength of the fibre-reinforced composite material, theremay at the same time be insufficient effect in enhancing the toughnessbetween layers of fibre-reinforced composite material. If theinterlaminar thickness exceeds 70 μm, the intralaminar fibre becomes toodense and, with the effects of stress concentration, there may belowering of the tensile strength and compression strength.

In the present invention, as the honeycomb core, a Nomex honeycomb corecomprising aramid paper impregnated with phenolic resin is preferred inthat it is possible to form a high-strength structure while still beinglight in weight. With regard to the cell size of the honeycomb core,there can be favourably employed material of cell size 3 to 19 mm. Inaddition, it is also possible to use an aluminium honeycomb, a glassfibre-reinforced plastic (GFRP) honeycomb, a graphite honeycomb, a paperhoneycomb or the like.

The honeycomb sandwich panel can be fabricated by a co-curing method inwhich a number of layers of prepreg are laid on both faces of thehoneycomb core and, while curing the resin, adhesion to the honeycomb iseffected. Again, the honeycomb sandwich panel can be fabricated byvacuum bag fabrication, autoclave fabrication using a vacuum bag,pressing or the like, but autoclave fabrication is preferred forobtaining a honeycomb sandwich panel of higher product quality andperformance.

EXAMPLES

Below, the present invention is explained in still more specific termsby means of examples. In the examples and comparative examples, thefollowing methods were employed for the production of the cured epoxyresin materials, the production of the prepregs, the production of thecomposite materials, and the measurement of the various properties.

<Glass Transition Temperature Tg of the Cured Material>

This is measured by a differential scanning calorimetry (DSC) method.The resin composition is heated for 2 hours at 180° C. and the curedmaterial obtained is employed as the measurement sample. The DSC curveis obtained at a rate of temperature rise of 10° C./minute.

Next, as shown in FIG. 1, from the DSC curve the temperature at thepoint of intersection of the base line tangent and the endotherm tangentis obtained, and so too the temperature at the end point of theendotherm is obtained. The Tg is taken as the mid-point between thesetwo values.

Here, as the measurement instrument, there is used a DSC2910 (modelnumber) made by TA Instruments.

<The Modulus of Rigidity G′_(R) in the Rubbery Plateau of the CuredMaterial>

This is measured by dynamic mechanical analysis (DMA). There is employeda sheet-shaped moulded material (thickness 2 mm and width 10 mm)obtained by injecting the resin composition into a frame, which has beengiven a suitable mould-release treatment, and then heating for 2 hoursat 180° C. Evaluation is performed by DMA under conditions comprising aspan length of 40 mm, rate of temperature rise of 5° C./minute,torsional vibration frequency 0.5 Hz and strain 0.1%. In this evaluationmethod, the torsional rigidity G of the resin is measured in the regionfrom the Tg extending to the rubbery plateau, as shown in FIG. 2. Thetorsional rigidity G in the rubbery plateau which is shown followingdamping of the torsional rigidity G by the glass transition is taken asG′_(R).

Here, the measurement instrument used is a viscoelastic measurementsystem “Ares” (model name) produced by Rheometric Scientific.

<Tensile Breaking Strain of the Cured Material>

The resin composition is injected into a frame which has been given asuitable mould-release treatment, and then curing carried out by heatingfor 2 hours at 180° C. in an oven to produce a sheet-shaped curedmaterial of thickness 2 mm.

Next, from this cured material, in accordance with the method describedin JIS K7113, there is produced a test-piece by means of a dumbbell typetest-piece processing machine, and this test-piece is fitted to a straingauge. Tensile testing is carried out at a rate of 1 mm/minute and thetensile breaking strain (%) determined.

<Production of a Prepreg>

The resin composition is coated onto release paper, to produce a resinfilm having a specified resin weight per unit area. The resin film islaid onto both faces of the reinforcing fibre and, while applying heatand pressure, impregnation by the resin composition is effected and aprepreg produced.

In the case of woven fabric prepregs, there is employed plain weavefabric CF6273H (woven material thickness 0.22 mm, fibre bundlewidth/thickness ratio 69.2, cover factor 99.7%) comprising the carbonfibre “Torayca (registered trade mark)” T700G-12K (number of fibres12000, tensile strength 4.9 GPa, tensile modulus 240 GPa, tensileelongation 2.1%) made by Toray Industries Inc, or plain weave fabricC07373Z (woven material thickness 0.27 mm, fibre bundle width/thicknessratio 14.9, cover factor 93.3%) comprising the carbon fibre “Torayca”T300G-3K (number of fibres 3000, tensile strength 3.5 GPa, tensilemodulus 230 GPa, tensile elongation 1.5%) made by Toray Industries Inc.,to produce prepregs of fibre weight per unit area 193 g/m² and resincontent 40 wt %.

In the case of unidirectional prepregs, there is used the carbon fibre“Torayca” T800G-12K (number of fibres 12000, tensile strength 5.9 GPa,tensile modulus 290 GPa, tensile elongation 2.0%) made by TorayIndustries Inc., or the carbon fibre “Torayca” T300B-3K (number offibres 3000, tensile strength 3.5 GPa, tensile modulus 230 GPa, tensileelongation 1.5%) made by Toray Industries Inc., to produce prepregs offibre weight per unit area 190 g/m² and resin content 36 wt %. ps <0°Tensile Strength of the Laminates (the Composite Material)>

Unidirectional prepregs prepared by the above method are arranged in thefibre direction to produce a 6-ply laminate, and then fabrication iscarried out in an autoclave under a pressure of 0.59 MPa for 2 hours at180° C. after heating-up at 1.5° C./minute.

The 0° tensile strength (MPa) of this laminates is determined inaccordance with JIS K7073.

<Compression Strength of the Laminates (the Composite Material>

Laminate of unidirectional prepreg, produced by the aforesaid method, isimmersed for 2 weeks in hot water at 71° C. and, after thoroughlyabsorbing water, the compression strength CHW (MPa) is determined at 82°C. in accordance with JIS K7076 by compression loading from the fibredirection.

<Edge Delamination Strength EDS of Laminates (Composite Material)>

Ten sheets of unidirectional prepreg are laid in pseudo isotropicfashion in a (±25°/±25°/90°)s configuration, and a laminate produced byfabricating in an autoclave for 2 hours at 180° C. under a pressure of0.59 MPa, after heating-up at 1. 5° C./minute.

When subjecting this laminate to tensile testing in accordance with JISK7073, the strength when edge delamination is produced is measured andthis is taken as the sheet edge delamination strength EDS (MPa).

<Compression Strength of Laminates (Composite Material) After ImpactCAI>

24 sheets of unidirectional prepreg are laid in pseudo isotropic fashionin a (±45°/0°/−45°/90°)3s configuration, and a laminate produced byfabricating in an autoclave for 2 hours at 180° C. under a pressure of0.59 MPa, after heating-up at 1.5° C./minute.

From this laminate, a sample of length 150 mm×width 100 mm is cut out,subjected to a drop-weight impact of 6.7 J/mm at the sample centre inaccordance with ASTM D695, and the compression strength after impact CAI(MPa) determined.

<Prepreg Thickness>

The prepreg is affixed between two sheets of Teflon of smooth surfaceand then, over 7 days, the temperature is gradually raised to 150° C. tobring about gelling and curing, and a sheet-shaped cured materialproduced.

The cured material is cut from a direction perpendicular to the faceaffixed to the Teflon and, after polishing the cut face, a photograph istaken at a magnification of at least 200 with an optical microscope, insuch a way that the upper and lower faces of the prepreg are within thefield of view.

By this procedure, at five locations in the widthwise direction of thecross-sectional photograph, the spacing between the Teflon sheets ismeasured and the average (n=5) is taken as the prepreg thickness.

<Proportion of Fine Particles in the Prepreg>

For both faces of the prepreg, lines are drawn parallel to the prepregsurface at positions of depth corresponding to 20% of the thickness.

Next, in each case, the total area of the fine particles present betweenthe line and the prepreg surface, and the total area of all the fineparticles observed over the entire prepreg thickness, are respectivelydetermined. Then, the proportion of fine particles present within adepth, from the prepreg surface, corresponding to 20% of the total 100%prepreg thickness, is calculated.

Here, the total area of the fine particles is determined by calculationfrom the weight when the fine particle regions are cut from thecross-sectional photograph.

Now, in cases where determination is difficult following photographingof the fine particles dispersed in the matrix resin, there may beemployed a means for staining the fine particles.

<Amount of Resin Fine Particles Added>

By means of a solvent (here N-methylpyrrolidone was employed) which doesnot substantially dissolve the resin fine particles but does dissolvethe matrix resin), only the matrix resin component is completelydissolved from a weighed amount of prepreg. The fine particles obtainedby filtering the washing liquid with a filter of suitable pore size areweighed, and the amount of resin particles added is determined.

<Average Particle Size of the Resin Fine Particles>

The prepreg is immersed for 24 hours in N-methylpyrrolidone solvent for24 hours at a room temperature of 25° C., and the resin dissolved out.Next, the solution is filtered using a filter of suitable pore size andthe fine particles separated. Furthermore, the fine particles are washedwith a sufficient amount of N-methylpyrrolidone. Thereafter, the fineparticles are photographed at a magnification of at least 1000 using ascanning electron microscope and particles randomly selected. Theaverage value (n=50) of the particle size (diameter of equivalentcircle) is taken as the average particle size of the fine particles.

<Composite Material Layer (Single Layer) Thickness>

Using the aforesaid laminate, the laminate is cut perpendicular to theplane of lamination and, after polishing the cross-section, this isphotographed at a magnification of at least 200 with an opticalmicroscope in such a way that at least three of the composite materiallayers are within the field of view.

From this cross-sectional photograph, there is selected one compositematerial layer where the fibre axis layer is in the horizontaldirection, and this is taken as the standard 0° layer. Between thecomposite material layers above and below the standard 0° layer, centrelines are drawn parallel to the fibre axis, and the spacing betweenthese two centre lines is measured. This procedure is carried out in atleast five locations in the laminate and the average (n=5) is taken asthe thickness of the composite material layer (single layer).

<Interlaminar Thickness >

In the aforesaid cross-sectional photograph, in the interlaminar regionsabove and below the standard 0° layer, 19 equi-spaced lines are drawn(within a set range) perpendicular to the 0° fibre axis. For theselines, the average (n=38) of the lengths of the segments producedbetween the reinforcing fibre in the layers above or below the standard0° layer and the reinforcing fibre in the standard 0° layer is taken asthe interlaminar thickness (see the sectional schematic diagram in FIG.3).

<Interlaminar State>

A laminate is produced by superimposing 24 sheets of prepreg inpseudo-isotropic fashion in a (±45°/0°/−45°/90°)3s configuration, andfabrication is performed at 1.5° C./minute and keeping for 2 hours at180° C. in an autoclave under a pressure of 0.59 MPa. The cross-sectionis then observed with an optical microscope and the state of the fineparticles in the laminate interlayer regions is noted.

<CDP Between Skin Panel/honeycomb Core>

(1) Sample Lamination

As the honeycomb core there is used a Nomex honeycomb SAH1/8-8.0 (madeby Showa Hikoki K.K., code: SAH1/8-8.0, thickness 12.7 mm). Furthermore,using the aforesaid woven material prepreg, a (±45°)/(±450°) two-plysymmetrical laminate structure is formed both above and below thehoneycomb. The dimensions of the honeycomb and prepreg here are 40 cm(shortwise direction)×50 cm (longwise direction), and the prepreg islaminated such that the shortwise direction is the honeycomb core ribbon(L) direction and the prepreg warp direction.

(2) Sample Fabrication

The following procedures are employed.

(a) The unfabricated body comprising the prepreg superimposed on thehoneycomb core is placed on an aluminium tool plate coated with releaseagent, for example “Freecoat” 44-NC (made by the Dexter Corporation).

(b) The unfabricated body is covered with nylon film and, with theregion within the nylon film (referred to below as the system interior)maintained under a vacuum, it is then introduced into an autoclave.

(c) The pressure inside the autoclave is raised to 0.15 MPa and then thepressure inside the system is normalized. Next, the pressure inside theautoclave is raised to 0.30 MPa, after which heating is commenced.

(d) With the pressure inside the autoclave held as it is, at 0.30 MPa,until the fabrication is complete, the temperature is raised to 180° at1.5° C./minute. It is then maintained at 180° C. for 2 hours and, whilethe resin is cured, adhesion to the honeycomb core is effected, afterwhich the temperature is lowered at 2° C./minute, to produce thehoneycomb co-cured fabricated body, that is to say the honeycombsandwich panel.

(3) Measurement of the Climbing Drum Peel Strength (CDP)

A sample is cut from the aforesaid fabricated body and, in accordancewith ASTM D1781, the CDP is measured between the honeycomb core and theskin panel on the aluminium tool plate side.

EXAMPLES 1 to 8 Comparative Example 1 and 2

In the examples and comparative examples, the following startingmaterial resins were employed.

[Starting Material Resins]

tetraglycidyl diaminodiphenylmethane, MY720 (code name, produced by CibaGeigy)

bisphenol A type epoxy resin, Epikote 825 (made by Yuka Shell EpoxyK.K., registered trade name)

bisphenol F type epoxy resin, Epiclon 830 (made Dainippon Ink &Chemicals Inc., registered trade name)

biphenyl type epoxy resin, Epikote YX4000H (made by Yuka Shell EpoxyK.K., registered trade name)

polyethersulphone, Victrex 100P (made by the Sumitomo Chemical Co.,registered trade name)

polyetherimide, Ultem 1000 (Made by GE Plastics Japan, registered tradename)

bisphenol S (made by the Konishi Chemical Co.)

3,3′-diaminodiphenylsulphone (made by the Wakayama Seika Kogyo Co)

4,4′-diaminodiphenylsulphone, Sumicure S (made by the Sumitomo ChemicalCo., registered trade name)

dicyandiamide, DICY7 (made by Yuka Shell Epoxy K.K., registered tradename)

3-(3,4-dichlorophenyl)-1,1-dimethylurea, DCMU99 (made by HodogayaChemical Co., trade name)

[Fine Particles]

crosslinked PMMA fine particles: Techpolymer MBX-20 (average particlesize 20 μm), MBX-40 (average particle size 40 μm), MBX-8 (averageparticle size 8 μm) (trade names; produced by the Sekisui Plastics Co.

benzoguanamine/melamine resin fine particles, Epostar M30 (averageparticle size 3 μm) (made by the Nippon Shokubai Co., product code)

Resin compositions were prepared by kneading the aforesaid resins in akneader based on the formulations shown in Table 1. Next, in accordancewith the methods described above, laminates, prepregs and honeycombsandwich panels were produced, and their properties evaluated. Thedetails for each of the examples and comparative examples are showntogether in Table 1.

It is clear that, in the case of Example 1 for example, when compared toComparative Example 1 the 0° tensile strength, edge delaminationstrength EDS, compression strength after impact CAI and the climbingdrum peel strength CDP, which is an index of the peel strength, areenhanced, and furthermore, the compression strength CHW which is anindex of the wet heat resistance is maintained.

Furthermore, in Comparative Example 2, the Tg is less than 150° C. and,when compared to the examples, it is clear that the compression strengthCHW which is an index of the wet heat resistance is markedly loweredand, furthermore, the 0° tensile strength, edge delamination strengthEDS, compression strength after impact CAI and the climbing drum peelstrength CDP are also unsatisfactory.

Industrial Application Potential

In accordance with the present invention, it is possible to provide afibre-reinforced composite material which in particular can be used inapplications where high level properties are demanded in a hot and wetenvironment, and which is outstanding in its impact resistance andstrength characteristics such as tensile strength and compressionstrength, together with a thermosetting resin composition and a prepregwhich can be suitably used in the production of this fibre-reinforcedplastic material and which are outstanding in terms of their peelstrength to a honeycomb core.

TABLE 1 Examples 1 2 3 4 5 Matrix Composition [Epoxy Resin] Resin (partsby tetraglycidyl diaminodiphenylmethane 10 10 10 10 10 weight) bisphenolA type epoxy resin 50 50 50 50 50 bisphenol F type epoxy resin 40 40 4040 40 biphenyl type epoxy resin — — — — — [Other Starting MaterialResins] bisphenol S — — 6 6 6 polyethersulphone — — — — — polyetherimide8 8 8 8 8 [Curing agent] 3,3′-diaminodiphenylsulphone — — — — —4,4′-diaminodiphenylsulphone 35 35 35 35 35 dicyandiamide — — — — —3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) — — — — — [FineParticles] crosslinked PMMA fine particles (av. size 40 μm) — 7 — — —crosslinked PMMA fine particles (av. size 20 μm) — — 7 — — crosslinkedPMMA fine particles (av. size 8 μm) — — — 7 — BG/melamine resin fineparticles (av. size 3 μm) — — — — 7 glass transition temperature Tg (°C.) 164 164 168 167 165 rubbery plateau modulus of rigidity G′_(R) (MPa)8.9 8.9 7.4 7.3 7.2 tensile breaking strain (%) 11.2 10.1 14.3 14.4 14.6Unidirectional prepreg carbon fibre type T800G T800G T800G T800G T800Gproportion of resin fine particles within 20% depth (%) — 99 95 80 54Laminate 0° tensile strength (MPa) 3116 3181 3188 3186 3188 (compositematerial) hot wet compression strength CHW (MPa) 1296 1291 1295 12881293 edge delamination strength EDS (MPa) 441 477 464 445 437compression strength after impact CAI (MPa) 244 276 285 255 248interlaminar thickness (μm) 6 49 33 9 7 composite material layer(monolayer) thickness 196 193 189 188 192 Woven prepreg carbon fibretype T700GC T700GC T700GC T700GC T700GC proportion of resin fineparticles within 20% depth (%) — 96 97 86 56 Honeycomb sandwich panelclimbing drum peel strength CDP (N.m/m) 24 28 28 25 24 Examples CompExamples 6 7 8 1 2 Matrix Composition [Epoxy Resin] Resin (parts bytetraglycidyl diaminodiphenylmethane 10 10 10 65 20 weight) bisphenol Atype epoxy resin — — 50 20 40 bisphenol F type epoxy resin 40 40 40 1540 biphenyl type epoxy resin 50 50 — — — [Other Starting MaterialResins] bisphenol S 5 — 6 — — polyethersulphone 10 10 — — 10polyetherimide — — 8 8 — [Curing agent] 3,3′-diaminodiphenylsulphone 3333 — — — 4,4′-diaminodiphenylsulphone — — 35 43 — dicyandiamide — — — —3 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) — — — — 3 [FineParticles] crosslinked PMMA fine particles (av. size 40 μm) 10 10 — — —crosslinked PMMA fine particles (av. size 20 μm) — — 7 — — crosslinkedPMMA fine particles (av. size 8 μm) — — — — — BG/melamine resin fineparticles (av. size 3 μm) — — — — — glass transition temperature Tg (°C.) 177 173 168 218 147 rubbery plateau modulus of rigidity G′_(R) (MPa)7.0 9.1 7.4 10.6 8.3 tensile breaking strain (%) 16.2 11.7 14.3 4.7 12.3Unidirectional prepreg carbon fibre type T800G T800G T300B T800G T800Gproportion of resin fine particles within 20% depth (%) 96 97 97 — —Laminate 0° tensile strength (MPa) 3210 3185 2055 2751 3010 (compositematerial) hot wet compression strength CHW (MPa) 1311 1320 1308 1310 910edge delamination strength EDS (MPa) 513 472 440 352 355 compressionstrength after impact CAI (MPa) 290 278 284 205 208 interlaminarthickness (μm) 9 52 29 7 6 composite material layer (monolayer)thickness 193 191 193 199 198 Woven prepreg carbon fibre type T700GCT700GC T300B T700GC T700GC proportion of resin fine particles within 20%depth (%) 96 97 93 — — Honeycomb sandwich panel climbing drum peelstrength CDP (N.m/m) 31 28 22 12 18

What is claimed is:
 1. An epoxy resin composition for a fiber-reinforced composition material, which is an epoxy resin composition where the glass transition temperature Tg of the cured material obtained by heating for 2 hours at 180° C. is at least 150° C., and the modulus of rigidity G′_(R) in the rubbery plateau in the temperature region above the aforesaid Tg is no more than 10 MPa.
 2. An epoxy resin composition according to claim 1 where the tensile breaking strain of the cured material is at least 8%.
 3. An epoxy resin composition according to claim 1 where there is included 5 to 35 parts by weight of trifunctional epoxy resin and/or tetrafunctional epoxy resin per 100 parts by weight of total epoxy resin.
 4. An epoxy resin composition according to claim 1 where there is included 50 to 95 parts by weight of difunctional epoxy resin per 100 parts by weight of total epoxy resin.
 5. The epoxy resin composition according to claim 1, wherein the epoxy resin composition includes a constituent (C), wherein constituent (C) comprises fine particles of average particle size 3 to 70 μm which are substantially insoluble in the epoxy resin of the epoxy resin composition.
 6. An epoxy resin composition according to claim 5, wherein the average particle size of the fine particles of constituent (C) is in the range of 10 to 70 μm.
 7. An epoxy resin composition according to claim 1, which contains 1 to 20 parts by weight of bisphenol compound per 100 parts by weight of the total epoxy resin.
 8. A prepreg comprising continuous reinforcing fiber and the epoxy resin composition according to claim
 1. 9. A prepreg comprising the epoxy resin composition according to claim 5, wherein at least 90% of constituent (C) is contained within a depth from the prepreg surface of 20% of the average prepreg thickness.
 10. A prepreg comprising a reinforcing fiber impregnated in an epoxy resin composition, wherein the epoxy resin composition comprises the following constituents (A),(B) and (C): (A) trifunctional epoxy resin and/or tetrafunctional epoxy resin; (B) difunctional epoxy resin; (C) fine particles of average particle size 10 to 70 μm which are substantially insoluble in the epoxy resin of the aforesaid resin composition; and a curing agent, wherein the respective contents per 100 parts by weight of total epoxy resin in said resin composition are 5 to 35 parts by weight of constituent (A) and 50 to 95 parts by weight of constituent (B), and wherein at least 90% of constituent (C) is contained within a depth from the prepreg surface of 20% of the average prepreg thickness.
 11. The prepreg according to claim 10, wherein the average particle size of the fine particles of constituent (C) is 25 to 60 μm.
 12. The prepreg according to claim 8 or 10, wherein the reinforcing fiber is carbon fiber.
 13. The prepreg according to claim 9 or 10, wherein constituent (C) is thermoplastic resin fine particles.
 14. The prepreg according to claim 9 or 10, wherein constituent (C) has a crystalline structure and/or crosslinked structure.
 15. The prepreg according to claim 9 or 10, wherein constituent (C) is thermosetting resin fine particles.
 16. A fiber-reinforced composite material formed by laminating a plurality of prepregs according to claim 8 or claim
 10. 17. The fiber-reinforced composite material according to claim 16, wherein interlaminar regions comprising a resin layer are formed between the plurality of prepregs and wherein the average thickness of the resin layer formed in the interlaminar regions is in the range 10 to 70 μm.
 18. The fiber-reinforced composite material according to claim 16, wherein interlaminar regions are formed between the plurality of prepregs, and wherein the interlaminar regions comprise fine particles of average size 10 to 70 μm.
 19. The fiber-reinforced composite material according to claim 18, wherein the average particle size of the particles 25 to 60 μm.
 20. A honeycomb sandwich panel formed by laminating prepreg according to claim 8 or claim 10 on a honeycomb core and curing. 